This invention relates to the field of model railroads and more particularly to power supplys for realistically controlling the operation of model railroad engines.
Known model railroad power supplies are connected in a suitable manner to power the engine and typically have a rheostat of the like for adjusting the output voltage. The engine is usually started by turning the rheostat wiper to gradually increase the output voltage. The engine remains stationary until the output voltage becomes sufficiently high to overcome the friction of the engine, causing it to leap forward suddenly at a speed proportional to the output voltage. Further increase in the output voltage causes an increase in the model engine speed. Conversely, decrease in output voltage causes the model to slow down. Such model movement is not very realistic.
Rheostat power supplies also cause model trains to slow down unrealistically when the train goes up a grade because the increased engine current causes the output voltage to drop. To compensate for this added slowdown on grades, the hobbiest must adjust the rheostat.
Hobbiests have long desired to simulate actual railroad movement and have developed more advanced model railroad power supplies in the attempt to provide more realistic model motion. Several such power supplies are described in articles appearing in a model railroad magazine (see Model Railroader, February, 1962, pages 56-67, Model Railroader, January, 1965 pages 60 and 61 and Model Railroader, March, 1969). The author of these articles suggests that realistic acceleration and deceleration of a model railroad engine can be achieved by providing an exponential voltage waveform having pulses of a large amplitude superimposed thereon. The described power supply with its exponential waveform, however, permits engine acceleration or deceleration which is rapid during the first time constant of the exponential curve and slower during subsequent time constant periods. Actual railroad engines, however, have acceleration or deceleration curves which more closely approximate a straight line than an exponential curve. As such, the model railroad power supplies described in the above mentioned articles do not produce realistic results.
In addition, these power supplies have proven difficult to use with some model railroad engines because many circuit adjustments are required to achieve optimum results and these controls interact with each other making optimum adjustment difficult.
In view of the foregoing difficulties of the prior art, it is an objective of the invention to provide a power supply to operate a model railroad engine in a manner realistically simulating the movement of an actual railroad engine.
It is yet a further objective of the invention to provide a power supply for realistic control of a model railroad engine which will maintain a substantially constant output voltage as the engine loading on the supply varies.
It is a further objective of the invention to provide a power supply for realistically controlling a model railroad engine which includes an overload protection circuit to prevent circuit damages if the output load current exceeds a permissable maximum.
It is atill another objective of the invention to provide a power supply for realistic control of a model railroad engine including an open circuit indicator to indicate when no power is being drawn from the supply.
In achieving these objectives, the power supply according to the invention includes four principal function sub-sections, namely, a linear ramp generator, an output regulator, a pulse generator, and a pulse control, all of which respond directly or indirectly to an operation selector. The linear ramp generator and pulse generator respectively produce a linear ramp signal and pulses during periods of time when the model is either accelerating or decelerating. The linear ramp signal and the pulse sigals are summed at a summing node to form the input to the output regulator. The output regulator responds to the summed signal to produce a linear ramp signal with pulses superimposed thereon. The pulse control circuit samples the output from the output regulator and turns the pulse generator off whenever the output linear ramp voltage is greater than a given magnitude. The power supply, however, continues producing a linear ramp voltage until a selectable maximum magnitude is reached. Thereafter, the power supply produces a constant magnitude signal to run the model engine at a constant speed.
A feedback circuit samples the output voltage and generates a positive feedback signal when the output voltage falls. The positive feedback signal is fed into the summing node causing the output regulator to increase the output voltage thereby maintaining substantially constant model railroad engine speed.
An overload detector is also provided for detecting excessive current supplied by the output regulator to the model railroad track. Upon detecting an overload, the circuit causes the output regulator to remove power from the track and sets an overload indicator to advise the operator. Upon resetting the overload detector circuit, however, the power supply again operates normally.
The power supply also includes an open circuit detector which samples the current drawn from the power supply itself. If this current falls to zero, an indicator is activated to signify that power is not being drawn from the power supply. This condition may indicate an engine derailment on a powered segment of track, a wiring failure, that no engine is currently operating on the powered segment of the track or any other condition where no current is drawn from the power supply.